Considerable work has been done during the last decade or so in providing vegetable protein substitutes for meat, particularly using soy protein source material. Early efforts were devoted to the development and commercialization of meat substitutes derived from spun soy protein fibers. More recent effort has been devoted to developing a more economical route to meat substitutes through the extrusion processing of proteinaceous material, particularly defatted soy flour. This latter work is exemplified by the showing and description in U.S. Pat. No. 3,488,770 which teaches an extruded product made from defatted soy flour and having an open cell, plexilamellar structure. Even though this product, which is now commercially available as a meat substitute, contains the requisite nutritional protein, it is characterized by an unsatisfactory mushiness in texture, particularly in heat processed meat foods and most particularly in retorted canned meat foods. Thus, this existing art has not provided an entirely acceptable meat substitute. Therefore, it is the principal object of this invention to provide a meat substitute of requisite nutritional value, yet one which avoids the mushy textural character of the prior art extrusion product and provides instead an elongated fibrous mass-like structure more simulative of meat.
The present invention concerns a novel process for the extrusion of proteinaceous materials such as defatted oil seed protein flours and concentrates and mixtures thereof and containing at least 40% protein on a moisture-free basis. Examples of suitable proteinaceous materials include defatted flours and concentrates derived from soybeans, peanuts, cottonseed, sesame seed and the like. In particular, defatted soy flours and concentrates are most suitable.
In order to obtain an extruded proteinaceous product which simulates the textural characteristics of meat, particularly when heat processed in food product preparation, we discovered that modification of a conventional extruder as described in prior art is necessary. As an example of a conventional extruder, we used a Wenger X-25 extrusion device with the modifications described in the following detailed description. However, it should be understood that the practice of this invention is not limited to this particular extrusion device as long as the extruder is suitable for the modification as specified.